1. Technical Field
The present invention relates to a stacked crystal resonator, in particular to a method of manufacturing a crystal resonator of a stacked type in which a crystal plate with a resonating section formed thereon is stacked between a base and a cover.
2. Background Art
A stacked crystal resonator is widely employed particularly in portable electronic devices as a source of frequency reference or time reference because of its small size and light weight. Responding to the needs of the information-oriented society in recent years, consumption of stacked crystal resonators is high and consequently there is a demand for an improvement in the productivity thereof. An example thereof is a stacked crystal resonator in which a base and a cover are stacked on the two main surfaces of a framed crystal plate composed of a resonating section and a frame section that surrounds the resonating section.
3. Prior Art
FIG. 12 to FIG. 15 are drawings describing a conventional example of a stacked crystal resonator, wherein FIG. 12 is an exploded view thereof, FIG. 13A is a plan view of a wafer on which a large number of covers are formed, FIG. 13B is a plan view of a wafer on which a large number of framed crystal plates are formed, FIG. 13C is a plan view of a wafer on which a large number of bases are formed, FIG. 14 is an exploded view illustrating the superposition of the wafers, and FIG. 15 is a cross-sectional view (along the line XV-XV in FIG. 14) illustrating the superposition of the wafers.
The stacked crystal resonator 1 disclosed in Patent Document 1, as shown in FIG. 12, comprises a framed crystal plate 7 in which a resonating section 4 with a tuning fork-shaped planar outer dimension having two vibrating arms 3 extending from one side face of a base section 2 is surrounded by a frame 5, and the resonating section 4 and the frame 5 are joined by connecting sections 6, and further comprises a cover 8 and a base 9 which are bonded to the two main surfaces of the framed crystal plate 7 so as to seal-enclose the resonating section 4.
Exciting electrodes 10 are formed on the two main surfaces and two side surfaces of the vibrating arms 3 of the framed crystal plate 7 shown in FIG. 12. Furthermore, extraction electrodes 11 extend from the exciting electrodes 10 to the base section 2 of the resonating section 4. On the side surfaces of the base section 2 where the vibrating arms 3 are not formed, connecting sections 6 extend from the two side surfaces on mutually opposite sides, to the frame section 5, and the extraction electrodes 11 extend to the two main surfaces of the frame section 5 via the two main surfaces of the connecting sections 6.
Furthermore, the cover 8 shown in FIG. 12 is composed of crystal or glass, and a concave section 12a is formed in a region of the main surface opposing the resonating section 4.
Moreover, the base 9 is also composed of crystal or glass, and comprises a concave section 12b formed in a region of the main surface opposing the resonating section 4. Furthermore, auxiliary electrodes 13 are formed in parts of the base 9 which oppose the extraction electrodes 11, and the extraction electrodes 11 and the auxiliary electrodes 13 connect electrically by mutual contact. Moreover, the auxiliary electrodes 13, via a conducting path (not shown) on the inside surface of through holes 14 formed at the approximate center of the auxiliary electrodes 13, are electrically connected to mount terminals (not shown) formed on the opposite surface from the main surface opposing the framed crystal plate 7. The through holes 14 are filled with, for example, a gold-tin (Au—Sn) alloy.
In such a stacked crystal resonator, first, etching is conducted on a crystal wafer 15a shown in FIG. 13B to form a plurality of the framed crystal plates 7 and support sections 16a which connect the framed crystal plates 7 to the crystal wafer 15a. Furthermore, etching is conducted on the crystal wafer 15b shown in FIG. 13A to form the covers 8 and support sections 16b which connect the covers 8 to the crystal wafer 15b. At this time, half-etching is conducted on the covers 8 to form the concave section 12a shown in FIG. 13A. Moreover, etching is conducted on the crystal wafer 15c shown in FIG. 13C to form the bases 9 and support sections 16c which connect the bases 9 to the crystal wafer 15c. At this time, the through holes 14 and the concave sections 12b are formed in the bases 9. The concave sections 12a and 12b are formed in the wafers 15b and 15c by half-etching.
Next, by vapor deposition or sputtering, the exciting electrodes 10 and the extraction electrodes 11 are formed on the framed crystal plate 7 shown in FIG. 14, and the auxiliary electrodes 13, the mount terminals, and the conducting path inside the through holes 14 are formed in the base 9. Then, the crystal wafer 15a and the crystal wafer 15c are superposed onto the two main surfaces of the crystal wafer 15b. Subsequently, the two main surfaces of the frame 5 are joined to the base 9 and the cover 8 by siloxane bonding.
Next, the resonating section 4 is seal-enclosed by filling the through holes 14 with, for example, a gold-tin (Au—Sn) alloy and then performing heating. By this process, the individual stacked crystal resonators 1 connected to the crystal wafers 15a, 15b, and 15c by the support sections 16a, 16b, and 16c are formed. Finally, by applying pressing force to the base 9 or cover 8 of the stacked crystal resonator 1, the stacked crystal resonator 1 is broken out of the crystal wafers 15a, 15b, and 15c. In other words, the stacked crystal resonators 1 are separated into individual pieces from the crystal wafers 15a, 15b, and 15c by breaking the support sections 16a, 16b, and 16c. 
(Refer to Patent Document 1: Japanese Unexamined Patent Publication No. 2009-60479 (paragraph 0043; FIG. 4))